Improved rotary compressed-air operated motor



Jan. 10, 1956 a Hf 1'. WILLIAMS IMPROVED ROTARY COMPRESSED-AIR OPERATED uo'roa Filed Oct. 22, 1951 2 sheets-sheet 1 A TTOIPNF) Jan. 10, 1956 G. H. T. WILLIAMS IMPROVED ROTARY COMPRESSED-AIR OPERATED MOTOR Filed 001:. 22, 1951 2 Sheets-Sheet 2 ATTORNEY United States Patent IMPROVED ROTARY COMPRESSED-AIR OPERATED MOTOR George Henry Thomas Williams, St. Albans, England Application October 22, 1951, Serial No. 252,522

2 Claims. (Cl. 121-92) This invention is concerned with rotary compressed-air operated motors, an object being to provide a motor which gives increased efficiency in operation.

As at present constructed rotary compressed-air operated motors usually comprise a rotor shaft having four longitudinal slots therein in which steel blades are adjustably disposed the rotor being positioned within a shell of oval internal cross-section the arrangement being such that compressed air admitted through inlet ports and acting on the blades causes the rotor to turn. The action of centrifugal force due to the rotary movement of the rotor is relied upon to a great extent in present motors of this kind to hold the blades against the inside wall of the shell. It has however been found that centrifugal force alone is not sufiicient to hold the blades in position and it has therefore been proposed to provide air holes drilled into the corner of the rotor blade slots in order that air pressure shall act behind the blades to hold them in position. This arrangement is an improvement but it is not entirely satisfactory since for one thing air pressure is not exerted behind a blade except when the associated air hole is in communication with an inlet port. Another feature of motors as at present constructed is that the reliance on centrifugal force has led to the use of heavy steel blades disposed rather loosely in the slots. I have found that these heavy steel blades are in some respects a disadvantage since appreciable power is absorbed in returning them into the slots at the appropriate time in the cycle of operations. This consumption of power is clearly undesirable especially bearing in mind that the motor may be revolving at any 5000 revolutions per minute. Reliance upon centrifugal force also means that a shell with a substantially regular internal surface must be used, that is to say a shell of regular oval internal cross section otherwise the blades tend to leave the shell wall at the point where the lobe greatly increases. However I have found that the use of a shell having a regular oval internal cross-section introduces another disadvantage namely that the pressure exerted on a blade as soon as it has passed an inlet port in the shell is small since the rotor blade is not able to move outwardly sufliciently in the initial portion of the power part of the revolution owing to the flat internal shape of the shell (see for example Figure 1 of the drawings).

The present invention therefore relates to rotary compressed-air operated motors of the type comprising the following features:

1. A rotor shaft longitudinally slotted to receive rotor blades which are movable radially of the rotor shaft in order to follow the internal wall of a shell surrounding the rotor shaft.

2. Rotor blades disposed within the slots in the rotor shaft.

3. An outer shell surrounding the rotor shaft and having an internal shape so designed that a power chamber or chambers is/are provided enclosed by the rotor shaft, the shell and each of the rotor blades in turn.

4. An inlet port or ports in the shell through which 2,730,077 Patented Jan. 10, 1956 air under pressure may be supplied to the motor in order to act on therotor blades to turn the rotor shaft. 7

5. An exhaust port or ports in the shell through which the air may be allowed to escape.

6. An inlet chamber for connection to a source of compressed air through which compressed air may pass to the inlet port or ports.

According to the present invention there is provided a rotary compressed air operated motor of the type set forth comprising a rotor having a length considerably greater than its diameter, an outer shell also having a length considerably greater than its diameter and positioned to enclose the rotor, power chambers formed between the rotor and the interior wall of the shell each chamber having a sudden increase of area adjacent the inlet port of the chamber and a gradual decrease inarea towards'the exhaust port of the chamber, longitudinally extending radial slots in the rotor, a rotor blade disposed within each slot and slidable in a radial direction, a longitudinal axial hole in the rotor, means to introduce compressed air into the axial hole and a plurality of radial passages along the length of the rotor to connect the longitudinal hole with each slot so that the compressed air introduced into the longitudinal hole is ap plied directly behind and along the length of each blade to press the blades outwardly towards the inner wall of the shell whereby the blades are maintained in contact with the inner wall of the shell throughout each rotary cycle despite the sharp changes in internal diameter of the shell.

With this arrangement in accordance with the present invention compressed air passing through the rotor shaft presses the blades at all times to remain in positive contact with the shell wall which is an essential requirement for economic running of the motor. This arrangement also allows the rotor blades to be a snug fit in their slots which has the efiect of conserving the consumption of compressed air used for the purpose of maintaining the blades in position. The constant pressure of the air at the base of the blades also makes it possible to use much lighter blades thanheretofore since centrifugal force is no longer relied on and therefore light metal alloy blades or even blades of non-metals such as light fibre'may be used. Further since the blades are at all times during running'of the motor positively urged outwardly my experiments have shown that it is possible to depart from the regular oval shape for the internal cross-section of the shell and to use according to a further feature of the invention what I call a cam-shaped shell form arranged to give greater power especially during the initial stage of the power part of a cycle. In other words the internal shape of the shell is of cam form so arranged that a sharp increase in the internal radius of the shell occurs immediately a blade passes an inlet port in order to give greater power during the initial stage of the power part of a cycle. 7

In order that the invention may be clearly understood and readily carried into effect reference is now directed to the accompanying drawings of one simple embodiment of the invention which are diagrammatic and by way of example, constructional details not necessary to a clear understanding of the invention being omitted.

Figure 1 is a longitudinal sectional plan of a motor according to the invention with details omitted.

Figure 2 is a section of the rotor shaft on the line AA of Figure 1 looking in the direction of the arrow A with the shell in elevation also looking in the direction of the arrow A.

Figure 3 is also a section of the rotor shaft on the line AA of Figure 1 but looking in the opposite direction (arrow B) with the shell in elevation also looking in the direction of the arrow B.

In Figure la tool according to this invention is illus trated including a rotor shaft 1, and an enclosing shell 2, longitudinal slots 5 and rotor blades 6. The rotor shaft f is reclu c ed at the power takeoff end at 13' for connection to a: tool or other workpiece and at the air inlet end 14 where it abuts substantially flush against the inner surface of a rear cap 14 which is screwed on to a rear bearing 15. The cap 14 is surrounded by a machine coupling 16 screw-threaded externally at 17 for connection to a suitable casing (not shown) and internally at 13 for connection to a compressed air pipe line arranged to be coupled to a suitable sourse of compressed air; Compressed air entering the motor at the opening-19 follows the paths of the arrows 20 through an air" inlet chamber 21 to air inlet ports 22 in the rear bearing which communicate with air inlet ports 23 in the' shell 2. The rotor shaft 1 is drilled longitudinally at 24 to provide a central hole which communicates through a hole 25 in the r'ear cap 14' with the air inlet chamber 21. Radial holes 26 connect the central hole 24 with the slots 5 as shown more particularly in Figures 2 and 3.

in Figures 2 and 3 the direction of rotation is given as by the arrows and in Figure 2 exhaust ports 27 are shown through which the air passes out of the motor after having done its work. Also shown in Figures 2and 3 is the modified shape of the internal surface of the shell 2 which is given a double cam form with sharp increases in internal radii at 28 in order to increase the area of blade exposed to the compressed air as soon as possible after a blade has passed the inlet port. This double cam shape of the shell is made possible by the pressure constantly acting behind the blades and pushing them outwardly against the inner surface of the shell.

In operation consider Figure 3, as soon as a supply of compressed air is connected to the motor through the opening 19 pressure is applied to the blades through inlet ports-2'3 to urge the blades adjacent to the ports in the direction of the arrow 10. This turns the rotor shaft and as these two blades pass into the exhaust section of the revolution so that the air may flow out through the exhaust ports 27 the other two blades pass into the power part of the revolution and so on. V

I have found that the improved motor has increased efiiciency and can achieve speeds of over 7000 revolu= dons per minute when running light. These motors have many uses in industry for example they are very suitable for insertion into a tube of a boiler to'work a descaling tool.

The improved motor according to the invention also 4 increases the power available at normal speeds when under load because the greater area of blade exposed to the compressed air gives greater torque.

It should be mentioned that the embodiment of the invention illustrated'which includes fan blades is given as an example only and in practice any suitable number of blades may be used. Preferably there will be four or more such blades;

What I claim is:

1. A rotary compressed air operated motor of the type set forth comprising a rotor having a length considerably greater than its diameter, an outer shell also having a length considerably greater than its diameter and positioned to enclose the rotor, power chambers formed between the rotor and the interior Wall of the shell, inlet and outlet ports in said shell communicating with said chambers, the internal surface of the shell having a double cam formation with sharp increases in internal radii near the inlet ports so' as to give each chamber a sudden increase of area" adjacent the inlet port" of the chamber and a gradual decrease in area towards the exhaust port of the chamber, longitudinally extending radial slots in the rotor, a rotor blade disposed within each slot and slidable in a radial direction, a longitudinal axial hole in the rotor, means to introduce compressed air into' the axial hole and a plurality of radial passages along the length of the rotor to' connect the longitudinal hole witheach slot so that the compressed air introduced into the longitudinal hole is applied directly behind and along the length of each blade to press the blades outwardly towards the inner wall of the shell whereby the blades are maintained in contact with the inner Wall of the shell throughout each rotary cycle despite" the sharp changes in internal diameter of the shell.

2. A rotary compressed air operated motor according to claim 1. characterized in this that the longitudinal slots in the periphery of the rotor are diametrically opposed.

References Cited in the file of this patent UNITED STATES PATENTS 994,400 Holt June 6, 1911 1,010,956 Read et al Dec. 5', 1911 1,026,165 Hummel May 14, 1912 1,942,784 Terrill -2- Jan. 9,- 1934 2,222,689 SChOtt NOV. 26, 1940 2,255,781 Kendrick Sept. 16, 1941 2,475,224 Deitrickson July 5', 1949 

